1. Field of the Invention
The present invention relates to apparatus for coupling to the output shaft of a high speed drive motor and holding cutter bits that are caused to rotate at high rates of rotation with respect to a longitudinally-advanced work piece. More particularly, this invention pertains to a molding head, including peripheral cutter units, that provides multiple mechanisms for securing the cutter units against dislodgement during use.
2. Description of the Prior Art
The manufacture of molding generally involves the use of bits of predetermined cutting profile that are secured to rotatable cutting heads. A wood work piece is longitudinally advanced with respect to the cutting head, which is driven at high r.p.m. by the output shaft of an electric motor. The head is generally of symmetrical planar shape and includes means for accommodating at least one cutting bit at its periphery to engage the work piece as it is advanced.
The work environment, commonly involving motor speeds of up to 6000 r.p.m., is inherently subject to vibration. As the work piece is often advanced by hand, the operator is usually close at hand and numerous factors can subject him to danger. Generally, the cutting bits are formed separately from the head to permit their replacement with bits suitable for forming alternative cutting patterns. Due to the presence of high motor speeds and vibration, such bits must be safely secured against dislodgement in the presence of the centrifugal forces generated which have the potential to launch an object with sufficient speed to kill or maim. Another as danger can arise when the workpiece is manually advanced too rapidly with respect to the rotating head and bits.
An example of a prior art molding cutter head of the above-described type is illustrated in U.S. Pat. Ser. No. 2,731,991 of Cowley entitled "Molding Head With Cutter" and illustrated in FIG. 1. The plate-like head 10 is generally-symmetrical about a central aperture for receiving the output shaft of a drive motor and is mounted for clockwise rotation when oriented as shown in FIG. 1. It includes three equiangularly-spaced lobes 14, 16 and 18 for receiving and securing cutter bits 20, 22 and 24 respectively within edge slots 20', 22' and 24'. Bores within the lobes 14, 16 and 18 are arranged to receive bolts 20", 22" and 24" at the straight portions of the lobe profiles. The head 10 relies upon geometrical relationships between the slots and the bolts to overcome and, in fact, to utilize the centrifugal forces inherent in the rotation of the head to secure the bits 20, 22 and 24 from dislodging and flying outwardly during operation.
The reliance upon specific geometrical relationships between the bores for receiving the bolts and the slots for receiving the bits mandates the use of the lobed structure of the head 10. In use, driven at high rotation speeds, the straight edge portions of the lobes, which rotate in advance of their arcuate sections, tend to entrap air, thereby increasing vibration. Further, as the bits 20, 22 and 24 are each secured by a single bolt, each must be carefully tightened when changing bits. Thus, the careless operation of such a head can easily result in serious injury.